Poly(p-phenylene vinylene) (PPV) and its derivatives are among the most extensively studied organic semiconductive polymers. In spite of their processablity, high luminescence, and structural diversity, several challenges remain for further applications. As in many conjugated polymers (CPs), the fluorescence quantum yields of PPVs are substantially lower in the solid state due to interchain interactions. (a) Osaheni, J. A.; Jenekhe, S. A. J. Am. Chem. Soc. 1995, 117, 7389-7398. (b) Winnik, F. M. Chem. Rev. 1993, 93, 587-614. (c) An, B.-K.; Kwon, S.-K.; Jung, S.-D.; Park, S. Y. J. Am. Chem. Soc. 2002, 124, 14410-14415. Successful approaches to enhance the solid state emission efficiency of CPs include the incorporation of bulky side chains or rigid three-dimensional moieties. (a) Jakubiak, R.; Collison, C. J.; Wan, W. C.; Rothberg, L. J.; Hsieh, B. R. J. Phys. Chem. A. 1999; 103, 2394-2398. (b) Yang, J.-S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120, 11864-11873. Another key issue to be addressed is the tuning of the electron affinity of CPs in order to control their work functions and charge transporting properties. Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem. Int. Ed. 1998, 37, 402-428. Traditionally, atoms with lone pair electrons capable of electron donating or electron withdrawing groups (EWGs) connected directly to the π-system have been utilized to modify their electron affinity. (a) Hörhold, H.-H.; Helbig, M. Makromol. Chem., Macromol. Symp. 1987, 12, 229-258. (b) Leuze, M.; Hohloch, M.; Hanack, M. Chem. Mater. 2002, 14, 3339-3342. Direct attachment of EWGs can produce large effects and such polymers are also disclosed presently. Steric repulsion of bulky substituents at the phenylene or vinylene subunits, however, often induce deviations from planarity and decrease conjugation.
The fluorescent, semiconductive polymers of the present invention can be used in such applications as light emitting devices (LEDs). Recently, there has been reported an organic electroluminescence device (organic EL device) having a double-layer structure in which an organic fluorescent dye as a light-emitting layer is laminated with an organic charge transport compound used in photosensitive layer for electrophotography and the like. Japanese Patent Application Laid-Open (JP-A) No. 59-194393. Because organic EL devices with colored light emissions are obtained easily and have low voltage driving and high luminance as compared to inorganic EL devices, there have been reported trials regarding device structures, organic fluorescent dyes and organic charge transport compounds of organic EL devices. Jpn. J. Appl. Phys., 27, L269 (1988), J. Appl. Phys., 1989, 65, 3610.
Apart from organic EL devices using mainly organic compounds having a lower molecular weight, polymer LEDs using light-emitting materials having a higher molecular weight have been proposed. WO 9013148 published specification; JP-A No. 3-244630; Appl. Phys. Lett., 1991, 58, 1982. WO9013148 discloses in the Examples an EL device using a thin film of poly(p-phenylene vinylene) obtained by forming a film of a soluble precursor on the electrode and subjecting it to a heat treatment to convert the precursor into a conjugated polymer.
Further, JP-A 3-244630 has exemplified conjugated polymers soluble in a solvent and needing no heat treatment. Also, a polymeric light-emitting material soluble in a solvent and a polymer LED using the same has been reported. Appl. Phys. Lett., 1991, 58, 1982.
Soluble, fluorescent polymers are advantageous for forming films having large areas at reduced cost since the organic layer can easily be formed by coating methods, as compared to vapor deposition of low molecular weight materials. The mechanical strength of the resulting film is believed to be greater due to the higher molecular weight of the fluorescent polymers.
Conventionally, in addition to the above-described poly(p-phenylene vinylene), there have been reported polyfluorene, poly p-phenylene derivative and the like, as the light-emitting materials used in these polymeric LEDs. Jpn. J. Appl. Phys., 1991, 30, L1941; Adv. Mater., 1992, 4, 36.
In order to utilize the film-formable characteristics of a polymeric fluorescent substance by coating, there is needed polymeric fluorescent substances having excellent solubility in organic solvents. To realize the practical flat panel display, there is needed a polymer LED having high efficiency and long lifetime.
One object of the present invention is to provide fluorescent, semiconductive polymers having increased solubility in organic solvents, enhanced photochemical and thermal stability, and a polymer LED having high performance which can be driven at higher efficiency and longer lifetime using the fluorescent, semiconductive polymer.
Another application of the fluorescent, semiconductive polymers of the present invention is sensors, in particular, biosensors. Recent developments in the world political situation, exemplified by the disintegration of the Soviet Union, continued geopolitical pressures in the Middle East and Eastern Europe and the proliferation of terrorist activities throughout the world, have raised increased concerns about the use of chemical and biological warfare materials in local conflicts. The defense against chemical and biological warfare agents includes detection of potential threats, development and use of protective equipment, development of vaccination post-exposure prophylaxis measures and fabrication of structures providing barriers to the toxic agents which are suitable for decontamination procedures. Threat identification is imperative prior to engagement, during battle and after battle during decontamination procedures. In addition, chemical sensors for detecting chemical warfare materials are needed for treaty verification, demilitarization, environmental monitoring and characterization of materials acting as barriers to agent diffusion.
Existing methods of detection have proven inadequate. Existing methods for long-range threat identification, such as light detection and ranging (LIDAR), and for laboratory analysis of chemical warfare agents using gas chromatography to provide a chemical agent monitor (miniCAMS), light addressable potentiometric sensor (LAPS) or ion mobility sensor (IMS) technology, have all proven slow and cumbersome to carry out. A need exists for lightweight, high-sensitivity sensors having rapid response times.
Existing sensors have proven capable of meeting the requirements of several applications, but no sensor has provided the combined sensitivity and speed of response needed for each application. Needs exist for field-usable chemical and biological sensors for the detection of vapor and liquid dispersed chemical warfare agents, toxins of biological origin and aerosol dispersed pathogenic microorganisms. Existing instrumentation used in identifying chemical warfare agents rely on ion mobility spectroscopy or gas chromatography for detection. The Advanced Chemical Agent Detection/Alarm System (ACADA) uses ion-mobility spectroscopy to achieve sensitivities to Sarin and Soman on the order of 1 mg/m3 (170 parts per billion (ppb)) in ten seconds and 0.1 mg/m3 (17 ppb) in 30 seconds. In addition to the system's slow response and low sensitivity, the size and weight characteristics of the ACADA system (one cubic foot in volume and 25 pounds in weight) reduces the applicability of the system for distributed sensing or remote sensing applications. Sensors such as the miniCAMS system provide unparalleled sensitivity but require preconcentration times on the order of minutes. That response time is unsuitable for rapid detection of conditions that are immediately dangerous to life and health. Other existing methods use acoustic or optical/electrochemical methods of detection, such as surface acoustic wave (SAW)-based instruments and light addressable potentiometric sensors (LAPS). Neither method has proven effective in meeting the sensitivity and response times required. At best, the SAW instrument has demonstrated sensitivities to Sarin/Soman at 0.01 mg/m3 (1.7 ppb), but requires preconcentration times ranging from 2 minutes to 14 minutes. Needs exist for field-usable sensors that provide for highly-sensitive, rapid response measurements of the concentration of analytes in solution or in air.
The need still exists for stable, soluble, fluorescent, semiconductive polymers with unique electronic properties to meet the demands of the various applications described above.